The present invention relates generally to laser systems and more particularly to an adaptive laser system for ophthalmic use.
It has become common to employ lasers for eye surgery, including cataract surgery, refractive surgery, glaucoma surgery, corneal grafting retinal treatments, keratoplasty, and the like. More recently, ultrafast lasers, having an amplified output of at least 1 μJ per pulse and a duration of at least 250 fs have been used. “Aside from the technical benefits that come along with femtosecond lasers, there were new side effects that arose with the technology that are now better understood. The formation of a bubble layer occurs along the cutting plane, which in some cases leads to an escape of some bubbles into deeper stroma with the formation of an OBL [opaque bubble layer] . . . . These deeper bubbles may take a few hours to disappear, and if severe, may impair the aim of the eye tracker during surgery.” G. Reggiani-Mello, et al., Comparison of Commercially Available Femtosecond Lasers in Refractive Surgery, Expert Rev. Ophthalmol., 6 (1): 55-65 (Mar. 1, 2011). It is also problematic that bubbles can cause undesired tears in the cornea during surgery. Furthermore, K. Plamann, et al., Ultrashort Pulse Laser Surgery of the Cornea and the Sclera, J. Opt. 12, 084002 (Jul. 15, 2010), states that such bubbles are created due to nonlinear laser-tissue interaction processes caused by these femtosecond pulse lasers.
Additional challenges of femtosecond pulses are presented in paragraph numbers [0041]-[0054] of U.S. Patent Publication No. 2011/0028948 entitled “Optical System for Ophthalmic Surgical Laser” which published on Feb. 3, 2011, and is incorporated by reference herein. Additional ophthalmic procedures using lasers are disclosed in U.S. Patent Publication No. 2010/0324542 entitled “Method to Guide a Cataract Procedure by Corneal Imaging” which published on Dec. 23, 2010, U.S. Patent Publication No. 2010/0082017 entitled “Laser Modification of Intraocular Lens” which published on Apr. 1, 2010, and U.S. Pat. No. 7,131,968 entitled “Apparatus and Method for Opthalmologic Surgical Procedures Using a Femtosecond Fiber Laser” which issued on Nov. 7, 2006; all of which are incorporated by reference herein. It is noteworthy, however, that femtosecond lasers employed with conventional ophthalmic systems are extremely expensive and subject to mechanical failure related to the water cooling system, optical including damage to the SESAM saturable absorber, and electronics, if not regularly maintained which leads to significant lost opportunity costs and delays in surgical procedures when the lasers are being fixed.
In accordance with the present invention, an adaptive laser system for ophthalmic use is provided. In another aspect, a compact and relatively inexpensive laser is employed, with a direct diode pumped or Yb-doped gain element, in either a fiber or free space type configuration, without amplification, which emits a laser beam pulse having a duration less than 100 fs and an output energy less than 2 μJ per pulse. In yet another aspect, a titanium sapphire oscillator emits a laser beam pulse having a duration less than 30 fs and output energy less than 30 nJ per pulse. This low cost approach is advantageous for use in a multiple laser construction where two or more lasers can be arranged on the same machine and selected based on the type of surgical operation being performed, and/or used in a modularized manner as an instant replacement in the event that one laser fails.
In another aspect of the present system, non-linear optical (“NLO”) imaging uses multiphoton fluorescences and/or second and/or third harmonic generation, to create three-dimensional mapping of a portion of the eye in combination with automated feedback to assist with a surgical operation. This can advantageously replace optical coherence tomography (“OCT”) for determining the precise position of tissues and tracking performance of the system. In a further aspect of the present system, the patient interface uses laser induced markings or indicia to aid in focusing and/or calibration. Still another aspect employs temporal focusing of the laser beam pulse having a shorter than 100 fs duration. This advantageously assists in accurately controlling a depth of cut by a laser beam pulse without harming adjacent tissue. Temporal focusing is ideally suited for ultrafast laser pulses of less than 50 fs. A further aspect employs temporal focusing for diagnoses and/or treatment of retinal disease.
Moreover, automatic characterization and adaptive correction of non-linear optical distortions in a laser beam used for ophthalmic surgical procedures, which include spectral phase dispersion caused by the laser source, optics and the eye being treated as well as spatial distortion caused primarily by the eye being treated, are provided in an aspect of the present system. The adaptive control over the laser pulses gives the versatility of the system to, for example, ablate, cut, bleach, correct, modify, and non-invasively image ophthalmic tissues or an intraocular lens with the same unit regardless of their depth inside the eye. Another aspect employs a laser to make a generally accordion-like or other contiguous pattern cut on a diseased lens so that the lens can be removed as a single piece from the eye and thereafter replaced by an intraocular lens. A method of use and/or of manufacturing any of the preceding aspects is also provided.
The interest in using shorter pulses, despite the fact that they are more prone to dispersion, is the overall reduction in the amount of energy per pulse required to cause a modification or cut in the tissue for a particular surgical procedure. The present system uses laser pulses that are ten or more times shorter in duration than those conventionally used. The shorter pulses result in a ten-time reduction of average laser intensity used on the eye, making every procedure safer. This advantage is consistent with R. J. Thomas et al., A Comparative Study of Retinal Effects from Continuous Wave and Femtosecond Mode-Locked Lasers, Lasers in Surgery and Medicine 31, 9-17 (2002) who generally determined that damage to the retina can be directly related to the average intensity of the laser.
The present laser system is advantageous over conventional devices in that the present system should reduce, if not eliminate, undesired bubbles created during ophthalmic surgery when used with the characterization and correction control aspect. The considerably shorter pulses being considered in the present system have a pulse duration that is below that required for the creation of avalanche ionization, thereby reducing the possibility of forming necrotic tissue and reducing, if not preventing bubble formation. The elimination of bubbles would eliminate the conventional need to create a capsulotomy, which is used to allow the bubbles accumulated during the lens ablation. The capsulotomy procedure is not presently covered by U.S. health insurance. Phaco removal is presently the procedure that takes the longest. If the capsulotomy is not required and the laser operates at a much faster repetition rate, the present invention results in faster procedures. The specific femtosecond laser configuration of another aspect of the present system advantageously provides a considerably less expensive laser system than traditional femtosecond laser devices. This should increase the availability of these types of systems for surgical procedures in rural areas and less prosperous countries, and allowing for modularized backup lasers which also avoid down time during shipping and repair of a broken traditional laser. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.